The invention refers to a device for lateral containment of liquid steel between the crystallizing rolls of a casting machine for a steel strip.
Devices to contain the melted metal in the continuous casting machines for steel strip are already known.
Particularly well-known are the solutions that adopt oscillating connections, which allow the plates to self-align with the ends of the casting rolls.
More specifically, patent GB 2,296,883 considers the so-called pivoting elements positioned with respect to the action line of the pushing force produced by the liquid bath, so that the action of this force tends to make the plates rotate towards the lower part of the rolls.
With this solution the required alignment of the plates with respect to the rolls is obtained, but in some circumstances it can lead to operating difficulties. In fact, as the plates are free to rotate on their planes they expose different contact areas on the roll ends and, if the plates are already worn there may be wearing shoulders above the contact with the newly exposed faces, thus resulting in a poor closing contact, misalignment of the lateral barriers and losses of melted metal from the casting bath.
Patent GB 2,337,016 solves the above-mentioned rotation problem: in fact, thanks to the action of pins, the plate can freely oscillate both longitudinally and laterally to the rolls, but the rotation of the plate on its own plane is limited. But this solution does not allow uniform pressure distribution on the refractory surface, which is consequently subject to uneven wear; this wear is greater in certain areas and therefore the refractory needs to be replaced frequently.
In order to avoid these inconveniences the Applicant has studied, designed and developed the device described in this invention.
The device for lateral containment of liquid steel between two crystallizing rolls of a casting machine for a steel strip provides a connecting system between the trust unit and the confinement plates of the liquid bath which will ensure an excellent uniform pressure distribution on the surfaces on these plates in sliding contact with the rolls, allowing the plates to adapt well to lateral surfaces of the rolls in all working conditions.
Advantageously the invention provides a device to contain the liquid steel within the casting rolls, making it possible to optimize the contact conditions between the containing plates and the side faces of the corresponding rolls.
Advantageously, it is the maximum capacity of these plates is guaranteed to adapt to the side faces by using an oscillating connection between the plate thrust unit and the plates themselves.
In particular, this invention provides a uniform pressure distribution on the refractory skid in the whole contact area with the corresponding side surface of the roll so that in this area wear is uniform: the result is a longer use of this skid and a better prevention of melted metal losses. A longer refractory life leads to clear advantages in terms of cost and less stoppages of the casting machine for skid changing.
It is known from the state of the art that the casting rolls are cooled by internal water circulation and that the feeding zone for this cooling water has to be outside the part of the roll which is in contact with the solidifying strip in order to eliminate the thermal exchange transients and thus to guarantee uniform solidification along the generators that define this portion. In order to permit the introduction of the means able to contain the liquid steel bath up to the borders of the strip formation zone, it is necessary to reduce by a few millimeters the diameter of the end zones not in contact with the strip; in any case this difference in diameter is limited because the circumferential distribution of the cooling water must be as near as possible to the external surface of the roll. The lateral containment plates are therefore housed in the space created by the configuration of the casting rolls and rest on the shoulder or step resulting from the difference in diameter between the roll section in contact and the one not in contact with the liquid steel.
The so-called containment plate is made up of, with reference to only one side of the casting rolls, a refractory skid and a variety (three at least) of steel plates, spaced and connected by means of fixing elements, such as screws, welded pins or other.
The applicant has found that, in order to obtain the desired uniform distribution of the pressure on the refractory skid, it is possible to act on the arrangement of these fixing elements. More precisely, a staggered arrangement allows all the elements to be compressed by the thrusting force and, consequently, contact pressure distribution is more uniform.
Regarding the oscillating connection between the thrust unit and the plates, the applicant has conceived a ball joint with a particular manufacturing solution which allows the application point of the thrust force to be nearer to the contact surface between the plate and the roll side, thus minimizing the moment due to the friction on the refractory skid. For execution, a part of the ball has to be directly in contact with the adjacent metallic plate, thus eliminating the intermediate connection elements (pin and fork) typical of a traditional ball joint. This joint allows the casting skid to oscillate longitudinally and transversally to the casting roll, while the rotation of the skid itself on its own plane is hindered by an anti-rotation system.